Description
The goal of this assignment is to gain experience with both TCP and UDP socket programming in a clientserver environment (see Figure 1). You will use Python or any other programming language to design and implement a client program (client) and a server program (server) to communicate between themselves.
2 Assignment Specifications 2.1 Summary In this assignment, the client will send requests to the server to reverse strings (taken as a commandline input) over the network using sockets. This assignment uses a two-stage communication process. In the negotiation stage, the client and the server negotiate on a random port () for later use through a fixed negotiation port () of the server. Later in the transaction stage, the client connects to the server through the selected random port for the actual data transfer. 2.2 Signalling The signalling in this assignment is done in two stages as shown in Figure 2. Stage 1. Negotiation using TCP sockets: In this stage, the client creates a TCP connection with the server using as the server address and as the negotiation port on the server (where the server is listening). The client sends a request to get the random port number from the server, where it will then send the actual requests (i.e., the strings to be reversed). To initiate this negotiation, the client sends a request code (), an integer (e.g., 13), after creating the TCP connection. If the client fails to send the intended , the server closes the TCP connection. Once the server verifies the , it replies back with a random port number , where it will be listening for the actual requests. After receiving this , the client closes the TCP connection with the server. Stage 2. Transaction using UDP sockets: In this stage, the client creates a UDP socket to the server in and sends the first request, containing a string. On the other side, the server receives the string and sends the reversed string back to the client. Once received, the client prints out the reversed string and sends the subsequent string. Once the client sends all its strings and receives the corresponding replies, it sends the keyword “EXIT” to the server and the server closes the connection. Note that the server should continue listening on its for subsequent client requests. For simplicity, we assume, there will be only one client in the system at a time. Therefore, the server does not need to handle simultaneous client connections. 2.3 Client Program (client) You should implement a client program, named client. It will take these command line inputs: , , , , , …, in the given order. There can be any number of messages. 2.4 Server Program (server) You should also implement a server program, named server. The server will take as a command line parameter. The server must print out the value in the following format as the first line in the stdout: SERVER_PORT= For example, if the negotiation port of the server is 52500, then the server should print: SERVER_PORT=52500 2.5 Example Execution Two shell scripts named server.sh and client.sh are provided. Modify them according to your choice of programming language. You should execute these shell scripts which will then call your client and server programs. • Run server: ./server.sh • Run client: ./client.sh ‘A man, a plan, a canal— Panama!’ ‘Pull up if I pull up’ 3 Hints You can use the sample codes of TCP/UDP socket programming in Python from the Chapter 2 slides. Below are some points to remember while coding/debugging to avoid trivial problems. • Use port id greater than 1024, since ports 0-1023 are already reserved for different purposes (e.g., HTTP @ 80, SMTP @ 25) • If there are problems establishing connections, check whether any of the computers running the server and the client is behind a firewall or not. If yes, allow your programs to communicate by configuring your firewall software. • Make sure that the server is running before you run the client. • Also remember to print the where the server will be listening and make sure that the client is trying to connect to that same port for negotiation. • If both the server and the client are running in the same system, 127.0.0.1 (i.e., localhost) can be used as the destination host address. • You can use help on network programming from any book or from the Internet, if you properly refer to the source in your programs. But, remember you cannot share your program or work with any other student. 4 Procedures 4.1 Due Date The assignment is due on Friday, June 10, 2022, at midnight (11:59 PM).
4.2 Hand in Instructions Submit all your files in a single compressed file (.zip, .tar etc.) using LEARN in dedicated Dropbox. You must hand in the following files / documents: • Source code files. • Makefile (if applicable): your code must compile and link cleanly by typing “make” or “gmake”. • README file: this file must contain instructions on how to run your program, which undergrad machines your program was built and tested on, and what version of make and compilers you are using. • Modified server.sh and client.sh scripts. Your implementation will be tested on the machines available in the undergrad environment, e.g.,: • ubuntu2004-002.student.cs.uwaterloo.ca • ubuntu2004-004.student.cs.uwaterloo.ca You can learn more about these servers and how to access them here: https://uwaterloo.ca/computer-science-computing-facility/teaching-hosts 4.3 Documentation Since there is no external documentation required for this assignment, you are expected to have a reasonable amount of internal code documentation (to help the markers read your code). You will lose points if your code is unreadable, sloppy, not efficient, or lacks internal documentation. 4.4 Evaluation Work on this assignment is to be completed individually.
5 Additional Notes: 1. You have to ensure that both and are available. Just selecting a random port does not ensure that the port is not being used by another program. 2. All codes must be tested in the linux.student.cs environment prior to submission. 1. Run client and server on two different student.cs machines 2. Run both client and server on a single student.cs machine 3. Make sure that no additional (manual) input is required to run server or client. 4. You are expected to design a robust code that handles exceptions and does not crash abruptly.
